1. Field of the Invention
This invention relates to integrated circuit structures constructed on semiconductor substrates. More particularly, this invention relates to a process for treating damaged surfaces of low dielectric constant (k) carbon doped silicon oxide dielectric material prior to exposure to the atmosphere to inhibit subsequent moisture absorption by such damaged low k carbon doped silicon oxide dielectric material when exposed to the atmosphere.
2. Description of the Related Art
In the construction of integrated circuit structures, dielectric materials such as silicon oxide (SiO2) have been conventionally used to electrically separate and isolate or insulate conductive elements of the integrated circuit structure from one another. However, as the spacing between such conductive elements in the integrated circuit structure have become smaller and smaller, the capacitance between such conductive elements through the silicon oxide dielectric has become of increasing concern. Such capacitance has a negative influence on the overall performance of the integrated circuit structure in a number of ways, including its effect on speed of the circuitry and cross-coupling (crosstalk) between adjacent conductive elements.
Because of this ever increasing problem of capacitance between adjacent conductive elements separated by silicon oxide insulation, as the scale of integrated circuit structures continues to reduce, the use of other insulation materials having lower dielectric constants than conventional silicon oxide (SiO2) has been proposed. One such material is a carbon doped (carbon-containing) silicon oxide material wherein at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by carbon-containing organic groups. In its simplest form, such carbon-containing silicon oxide dielectric material may comprise a mono or dimethyl silicon oxide dielectric material, wherein at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by methyl (CH3-) groups. Such a methyl silicon oxide dielectric material has a dielectric constant (k) of about 2.9 and is, therefore, of great interest as a low k substitute for the conventional silicon oxide (SiO2) insulation material, which has a k value of about 4.
Other such low k carbon-containing silicon oxide dielectric materials include the multiple carbon-containing silicon oxide dielectric materials described and claimed in copending U.S. patent application Ser. No. 09/274,457 now U.S. Pat. No. 6,303,047 entitled LOW DIELECTRIC CONSTANT MULTIPLE CARBON-CONTAINING SILICON OXIDE DIELECTRIC MATERIAL FOR USE IN INTEGRATED CIRCUIT STRUCTURES, AND METHOD OF MAKING SAME, which was filed on Mar. 22, 1999, and assigned to the assignee of this invention, and the subject matter of which is hereby incorporated by reference.
While the substitution of one or more carbon-containing organic groups such as methyl groups, for some of the oxygen atoms bonded to the silicon atoms has a beneficial effect in the lowering of the dielectric constant of the low k carbon-containing silicon oxide dielectric material, therefore lowering the capacitance between conductive elements separated by such dielectric material, it has been found that the bond formed between the silicon atoms and the carbon-containing organic group is not as stable as the silicon-oxygen bond found in conventional silicon oxide (SiO2) materials.
In particular, for example, when surfaces of such a low k carbon-containing silicon oxide dielectric layer are exposed to etchants used to form openings therein, or to oxidizing or xe2x80x9cashingxe2x80x9d systems, which are used to remove a photoresist mask such as the typical photoresist mask made of organic material from the low k carbon-containing silicon oxide dielectric layer after formation of such openings therein, it has been found that the etching and oxidizing (ashing) processes can result in damage to the bonds (severance) between the organic moieties (e.g., such as methyl radicals), and the silicon atoms adjacent the surfaces of the low k carbon-containing silicon oxide dielectric layer exposed to such etching and/or oxidizing treatments.
The term xe2x80x9copeningsxe2x80x9d, as used herein, is intended to describe either vias formed through a dielectric layer between two layers of metal interconnects, or contact openings formed through a dielectric layer between devices on the substrate and a metal interconnect layer. This severance of the carbon-silicon bonds in the low k carbon-containing silicon oxide dielectric material, in turn, results in removal of such organic materials formerly bonded to the silicon atoms along with the organic photoresist materials being removed from the integrated circuit structure. The silicon atoms from which the organic radicals have been severed, and which are left in the damaged surface of the low k carbon-containing silicon oxide dielectric layer, have dangling bonds which are very reactive and become water absorption sites if and when the damaged surface is exposed to moisture.
This absorption of moisture by the damaged low k carbon-containing silicon oxide dielectric material, results in hydroxyl bonding to the dangling silicon bonds left from the severance of the carbon-silicon bonds in the damaged surface of the low k carbon-containing silicon oxide dielectric layer. This silicon-hydroxyl bond is not a stable bond and subsequent exposure to heat, e.g., during subsequent processing such as annealing, can result in severance of the silicon-hydroxyl bond, thereby causing water vapor formation which, for example, can interfere with subsequent filling of a via/contact opening or a damascene trench with metal filler material.
It would, therefore, be desirable to repair any damage done to the low k carbon-containing silicon oxide dielectric layer by the severance of the carbon-silicon bonds prior to any exposure of the damaged surface to moisture to thereby ensure against formation of unstable silicon-hydroxyl bonds in the damaged surface of the low k carbon-containing silicon oxide dielectric layer.
Damaged surfaces of a low k carbon-containing silicon oxide dielectric material are treated with one or more carbon-containing gases, and in the absence of an oxidizing agent, to inhibit subsequent formation of silicon-hydroxyl bonds when the damaged surfaces of the low k dielectric material are thereafter exposed to moisture. The carbon-containing gas treatment of the invention is carried out after the step of oxidizing or xe2x80x9cashingxe2x80x9d the resist mask to remove the mask, but prior to exposure of the damaged surfaces of the low k dielectric material to moisture. Optionally, the carbon-containing gas treatment may also be carried out after the initial step of etching the low k carbon-containing silicon oxide dielectric material to form vias or contact openings as well, particularly when exposure of the damaged surfaces of the low k dielectric material to moisture after the via etching step and prior to the resist-removing oxidation step is possible. The treatment of the damaged low k carbon-containing silicon oxide dielectric material with a carbon-containing gas may be carried out with or without the assistance of a plasma, but preferably will be carried out in the presence of a plasma.